Aquamarine is classified as a gemstone, prized for its distinctive blue-to-cyan color that evokes the clear waters of the sea. As a member of the beryl family, it is a durable and highly sought-after material in the gem trade.
The Mineralogical Identity of Aquamarine
Aquamarine is a variety of the mineral beryl, chemically defined as beryllium aluminum silicate (\(\text{Be}_3\text{Al}_2\text{Si}_6\text{O}_{18}\)). The crystals typically form in a hexagonal system, often exhibiting well-formed prismatic shapes.
The stone is rated between 7.5 and 8 on the Mohs scale of hardness, making it highly resistant to scratching and abrasion. While hard, aquamarine has imperfect cleavage, meaning a sharp blow along a specific internal plane could cause it to split.
Understanding Aquamarine’s Distinctive Color
The characteristic blue-green to pure blue coloration is caused by trace amounts of iron impurities. The color arises from iron ions substituting for aluminum within the crystal lattice. Ferrous iron (\(\text{Fe}^{2+}\)) is the primary cause of the blue hue, while ferric iron (\(\text{Fe}^{3+}\)) contributes a yellowish tint, resulting in a greenish-blue natural stone.
The deepest, most saturated blue colors, such as the Brazilian “Santa Maria” aquamarines, are the most valuable. To enhance the color, nearly all commercial aquamarine undergoes gentle heat treatment, typically between 375 and 450°C. This process converts yellowish ferric iron ions into the desired blue ferrous iron ions, removing unwanted green or yellow components. This permanent enhancement is a routine, accepted practice in the jewelry industry.
Practical Considerations for Aquamarine Jewelry
The durability afforded by the Mohs hardness rating makes it a suitable choice for various jewelry types, including rings and bracelets exposed to daily wear. Due to its clarity and color saturation, aquamarine is frequently cut into popular styles such as emerald cuts, ovals, and pears. Cut-cornered styles, like the emerald cut, are often preferred because they help protect the stone’s vulnerable corners from chipping.
For routine care, the safest method is to clean the jewelry using warm, soapy water and a soft brush. Owners should avoid exposing the stone to harsh chemicals, such as hydrofluoric acid, which can attack the beryl structure. Ultrasonic cleaners are usually safe for stones free of liquid inclusions or internal fractures, but steam cleaning is not recommended due to the potential for cracking if imperfections exist.